Vacuum whirler for applying thin and uniform coating of an emulsion on a wafer



Feb. 11, 1969 K 5, BALAlN ET AL 3,426,727

VACUUM WHIRLER FOR APPLYING THIN AND UNIFORM COATING OF AN EMULSION ON AWAFER Filed Oct. 21, 1965 Sheet Of 2 FIGJ FIG-3 Feb. 11, 1969 5, BALAINETAL 3,426,727

VACUUM WHIRLER FOR APPLYING THIN AND UNIFORM COATING OF AN EMULSION ON AWAFER Filed Oct. 21, 1965 sheet 2 or2 FIG. 6

f/ire/ifdr maxi cud wazg 7%)[63/6 VACUUM WHIRLER FOR APPLYING THEN AND 1Claim ABSTRACT OF THE DISCLOSURE A vacuum whirler for applying a thinand uniform coating of an emulsion on a wafer, in which a rotor having ahorizontal, perforated top member is carried on a vertically mountedspindle rotatively driven by a motor, wherein the rotor is provided withfan blades for creating, when the spindle is driven in rotation, avacuum within the rotor causing a suction effect on the perforations inthe rotor top member for holding the wafer to be coated, thus enabling asingle motor to serve both for rotating the spindle and for creating therequired vacuum.

This invention relates to a vacuum whirler, more particularly of thekind used for applying a thin and uniform coating of an emulsion on awafer such as a semiconductor slice.

It is well known that the photolithographic (photornaskiug and photoetching) process is one of the key processes in the manufacture ofmodern semiconductor devices. In a photo-lithographic process, animportant step is that of applying a very thin coating of aphotosensitive emulsion, such as are available under the trade namesKodak Photo Resist and Kodak Metal Etch Resist. An essential requirementof such a coating is that it should be thin, uniform and adherent.

Said coating is usually applied by spreading the emulsion on the waferand spinning it, so as to utilize the centrifugal force for the purposeof uni-form spreading. The technique of spreading the photo-resist bycentrifugal force is preferred for accurate and fast work. In order toutilize this technique for semiconductor technology where the use ofvery thin and brittle substrates is encountered, a proper whirler(spinner) with a mechanism to hold the substrate by vacuum is required.Thus there is a need for a vacuum whirler which spins as Well as holdsthe substrate by vacuum.

The conventional vacuum whirler for the purpose mentioned has, incombination, (i) a motor to spin the rotor on which the substrate ispositioned, (ii) a vacuum device including another motor to create thenecessary vacuum to hold the substrates, and (iii) a high speed vacuumseal.

The conventional vacuum whirler as aforesaid suffers from variousdrawbacks, such as (i) that it necessitates the use of two separatemotors, viz. one to spin the rotor on which the substrate is positioned,and the other to create the necessary vacuum to hold the saidsubstrates; (ii) that it necessitates the use of a high speed vacuumseal; and (iii) that it involves a complicated design and is expensiveto manufacture.

This invention has for its object improvements whereby these drawbacksmay be obviated and certain additional advantages may be realised.

With this object in view, this invention consists of an improved vacuumwhirler for applying a thin and uniform coating of an emulsion on awafer, which whirler consists of a rotor mounted on a spindle adapted tobe spun or rotated by means of a high speed motor, the said rotor havinga perforated top on which the said wafer may be securely positioned as aresult of suction of air through the said perforations, and having alsoa suction creating means such as a paddle wheel fan fitted on the saidspindle immediately below the perforated top of the said rotor.

The improved vacuum whirler as aforesaid is provided with additionalmeans such as those mentioned below:

(i) a housing for the vacuum whirler, including its high speed motor;

(ii) a top cover for the said housing so as to cut off completely straylight that might otherwise fall on the rotor during the formation of thecoating;

(iii) a bowl for collecting extra liquid which may separate from thecoating emulsion as it is spread on the wafer by centrifugal force;

(iv) a mechanical brake to stop the rotor quickly, thereby reducing thetime needed for the completion of each coating operation; and

(v) levelling screws for adjusting the level of the vacuum whirler.

This invention will now be more particularly described with reference tothe accompanying drawings, wherein:

FIG. 1 is a schematic layout of an improved vacuum whirler according tothis invention.

FIG. 2 is an isometric view of the rotor of the said whirler, includingthe blades of the paddle wheel fan provided for creating suction.

FIG. 3 is a section on AA of FIG. 2.

FIG. 4 is a section on BB of FIG. 3.

FIG. 5 shows the details of mechanical brake mechanism provided forstopping the rotor.

FIG. 6- is a view, partly in section, showing a modified disposition ofthe rotor in relation to the high speed working of the vacuum whirler.

The vacuum whirler illustrated in the drawings consists of a rotor Imounted on a spindle 2 adapted to be spun or rotated by means of a highspeed motor 3, and it has a perforated top 4 having perforations 5.

Immediately below the said perforated top 4 and fitted on the saidspindle 2, is a paddle wheel fan 7 with blades so shaped as to suck inair through the said perforations 5, when the spindle 2 is spun rapidly.

The perforated top 4 is adapted to hold a wafer 8 securely in positionas a result of the suction created by the paddle wheel fan 7.

The said rotor 1 together with the motor 3 is provided with a metalhousing 9 having a top cover 10 adapted to cut off completely straylight from falling on the said rotor 1.

A bowl 11 is provided around the perforated top 4, for collecting extraliquid which may separate from the coating emulsion as it is spread onthe wafer 8 by centrifugal force.

The said vacuum whirler is provided with a brake mechanism which, asshown in FIG. 5, consists of a brake shoe 15 provided on a pivoted bentlever 16, which, at its remote end, is provided with a brake controlknob 17 of a rod 18 passing through push bearings 19, and with a spring20 which serves as the fulcrum for the operation of the said bent leverfor applying the brake to the rotor 1, or for releasing the brake fromthe said rotor 1.

The vacuum whirler is also provided with a variac 21 whereby the speedof the high speed motor 3 may be regulated tosuit requirements, and withlevelling screws 22.

It will be seen that a vacuum whirler as shown in the drawings willprovide various advantages such as:

(i) That both the rotor and the suction producing means are operated byone and the same motor, and therefore, there is no need for two separatemotors for operating them as in conventional whirlers.

(ii) As the wafer or like substrate will be held in position by thevacuum created underneath thereof, it will be pOssible to apply thecoating on its entire surface.

(iii) It will not be necessary to provide a high speed vacuum seal.

(iv) The mechanical brake provided for stopping the rotor quickly, willeconomise the time needed for a complete coating process.

(v) The top cover will facilitate the utilisation of the vacuum whirlerfor coating very senstive photo-resist emulsions.

(vi) The variac will enable a smooth adjustment of variable andreproducible speeds of the rotor.

(vii) The design of the whirler is quite simple and compact.

Instead of mounting the rotor member directly in line with the drivemotor a high speed centrifugal whirler may include a pulley and drivebelt connection as shown in FIG. 6 of the drawings.

What we claim is:

1. A vacuum whirler for applying a thin and uniform coating of anemulsion on a wafer, comprising a spindle, means supporting said spindlefor rotation about a vertical axis, a rotor mounted on the upper end ofsaid spindle for rotation therewith, said rotor having fixed withrespect thereto a perforated horizontal top member upon the perforatedsurface of which said wafer is supported and a fan member horizontallydisposed beneath 4 said perforated top member and fixedly mounted onsaid spindle whereby to effect a vacuum beneath said perforaated topmember when said spindle is rotated and whereby suction elfected throughthe perforations retains said wafer on the perforated surface, and meansfor rotating said spindle whereby to whirl said wafer and to effect saidsuctionretention of the water on the perforated surface.

References Cited UNITED STATES PATENTS OTHER REFERENCES IBM TechnicalDisclosure Bulletin Vacuum Spintable, by F. H. Masterson, vol. 5, No. 5,October 1962, pp. 7, 8.

MORRIS KAPLAN, Primary Examiner.

US. Cl. X.R.

